Effect of Proton Conduction on the Charge Storage Mechanism of a MOF as a Supercapacitor Electrode
Ling-Di Ye, Farzaneh Rouhani, Hamed Kaviani, Qian Miao, Xiaoqing Cai, Ali Morsali, Mao‐Lin Hu
Abstract
The current study aims to examine the charge storage mechanism of an amine-decorated metal–organic framework (TMU-60), as a supercapacitor electrode material, and explore the effect of proton conductivity on the supercapacitive performance of this electrode. To investigate the role of proton conductivity in charge storage capacity, Na2SO4 was selected as the base electrolyte at two pH levels (3 and 6). A high specific capacitance of 530 F·g–1 was achieved at 7 A·g–1 for the aqueous electrolyte at pH = 3, while the specific capacitance of the electrolyte decreased by 30% at pH = 6. The smaller sphere radius of H+ than Na+ and its higher ionic mobility in the narrow TMU-60 pores boosted charge transfer due to the higher ion penetration into the electrolyte/electrode interface. Furthermore, the presence of amines in proper orientation within the pores enhanced ion transport and ion mobility. The results obtained from cyclic voltammetry (CV) and electrochemical impedance spectroscopy for the electrodes at both pH values revealed that increasing the pH level elevated charge-transfer resistance. The constructed framework could tolerate high ranges of scan rates (200–1000 mV·s–1), and its semi-rectangular CV curves displayed a capacitance retention of 92.3% after over 4000 cycles.